Such a switching network is used in central exchanges, particularly in telephone central exchanges, to form connections between several subscribers. As it is usually assumed that only a certain portion of the connected subscribers are simultaneously busy, a concentrator is connected between the subscribers and the actual exchange, this concentration also comprises a switching network.
A space-division switching network comprises a plurality of switches which are layed out as a matrix and located at crosspoints of line and column conductors which are connected to the input and the outputs, respectively, the relevant crosspoint switch being closed to effect a desired connection. Such a switching network must indeed only switch low-frequency signals but its construction is nevertheless quite complicated. With a time-division switching network the inputs are cyclically scanned and read at different instants via a time-division multiplex line. Generally, only one single time-division multiplex output is then available.
With a concentrator in particular, a number of subscribers lines is concentrated at a considerably lower number of output lines, which are only then connected to the actual exchange to make a highest possible efficient use of this exchange. The concentrator must be of as simple a construction as possible, to save indeed cost and design effort.